Dram array architecture with row hammer stress mitigation

ABSTRACT

An apparatus includes a plurality of main word line circuits. Each main word line circuit drives a respective global word line to one of an active state value, an intermediate voltage state, or a pre-charge state. The intermediate voltage state voltage is below the active state voltage and above the pre-charge state voltage. The memory device also includes a plurality of sub-word line drivers. Each sub-word line driver is connected to a corresponding global word line and configured to drive a respective local word line between the corresponding global word line voltage and a low voltage value. The apparatus further includes a plurality of phase drivers. Each phase driver is connected to a predetermined number of sub-word line drivers, where each of the predetermined number of sub-word line drivers connects to a different global word line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/399,283, filed Apr. 30, 2019; which is incorporated herein byreference in its entirety.

This application contains subject matter related to an U.S. patentapplication by Charles L. Ingalls et al., titled “FX DRIVER CIRCUIT”.The related application is assigned to Micron Technology, Inc., and isidentified as U.S. patent application Ser. No. 16/399,159, filed Apr.30, 2019. The subject matter thereof is incorporated herein by referencethereto.

This application contains subject matter related to an U.S. patentapplication by Charles L. Ingalls et al., titled “SUB-WORD LINE DRIVERCIRCUIT”. The related application is assigned to Micron Technology,Inc., and is identified as U.S. patent application Ser. No. 16/399,197,filed Apr. 30, 2019. The subject matter thereof is incorporated hereinby reference thereto.

This application contains subject matter related to an U.S. patentapplication by Tae H. Kim et al., titled “MAIN WORD LINE DRIVERCIRCUIT”. The related application is assigned to Micron Technology,Inc., and is identified as U.S. patent application Ser. No. 16/399,235,filed Apr. 30, 2019. The subject matter thereof is incorporated hereinby reference thereto.

TECHNICAL FIELD

Embodiments of this invention relate to the architecture of a DRAMmemory device and methods of mitigating row hammer stress in the DRAMmemory device.

BACKGROUND

Memory devices are widely used to store information related to variouselectronic devices such as computers, wireless communication devices,cameras, digital displays, and the like. Memory devices are frequentlyprovided as internal, semiconductor, integrated circuits and/or externalremovable devices in computers or other electronic devices. There aremany different types of memory, including volatile and non-volatilememory. Volatile memory, including random-access memory (RAM), staticrandom access memory (SRAM), dynamic random access memory (DRAM), andsynchronous dynamic random access memory (SDRAM), among others, mayrequire a source of applied power to maintain its data. Non-volatilememory, by contrast, can retain its stored data even when not externallypowered. Non-volatile memory is available in a wide variety oftechnologies, including flash memory (e.g., NAND and NOR) phase changememory (PCM), ferroelectric random access memory (FeRAM), resistiverandom access memory (RRAM), and magnetic random access memory (MRAM),among others. Improving memory devices, generally, may includeincreasing memory cell density, increasing read/write speeds orotherwise reducing operational latency, increasing reliability,increasing data retention, reducing power consumption, or reducingmanufacturing costs, among other metrics.

Memory devices employ a variety of signals within the various circuitsof the memory device. Signal drivers for applying the signals to signallines are in common use in electronic devices, such as integratedcircuits. One such signal driver can be used to apply voltages to wordlines in an array of memory cells. The word lines may extend through amemory cell array from a set of global word line drivers (also referredto herein as “main word line drivers” and “MWDs”). The global word linedriver may selectively actuate each of the word lines responsive to thememory device receiving a row address corresponding to the word line.Each of the memory cells in the row corresponding to the received rowaddress then applies stored data to a respective sense amplifier.

Some semiconductor memory devices, such as DRAM, store information ascharge accumulated in cell capacitors (“cells”), with the cellsorganized into rows. In some cases, charge applied to cells in one rowcan interfere with charge in one or more adjacent “victim” rows or cellscan otherwise lose their charge, an occurrence referred to as “leakage.”Certain instances of leakage can occur when memory rows experience “rowhammering,” which is when a row is repeatedly driven to an active levelin a short time (e.g., over a duration less than that between sequentialrefresh operations) and the activations affect one or more adjacentvictim rows. This can result in changes to cell charges in the victimrows, putting the information stored there at risk.

Various memory systems use one or more strategies to address leakage,such as row hammer stress mitigation or target row refreshing (TRR). Rowhammer stress mitigation can include a host or controller automaticallyperforming refresh operations on victim rows on a random or periodicbasis. In some embodiments, row hammer stress mitigation can includecontrolling the local word line voltage such that, when going from anactive level to a pre-charge or standby level, the local word linevoltage is paused at an intermediate voltage level for a predeterminedtime period. By pausing at an intermediate voltage, adjacent memory rowsdo not experience the effects of a rapid change in voltage levels andthe row hammer stress can be mitigated.

Each of the word lines extending through the array may be relativelylong and, as a result, may have substantial capacitance. Furthermore,the word lines may be fabricated of polysilicon, which may have arelatively high resistance. The combination of the relatively highcapacitance and relatively high resistance of the word lines may make itdifficult for the global word line driver to quickly switch signallevels on the word lines, particularly in portions of the memory cellarray that are more distant from the global word line driver. Toalleviate this problem, it is conventional for memory cell arrays to bedivided into smaller memory cell arrays, and to fabricate local wordline drivers (also referred to herein as “sub-word line drivers” and“SWDs”) between at least some of these smaller memory cell arrays. Thelocal word line drivers may receive substantially the same signals thatare used to control the global word line drivers to drive the word linesso that they may apply the same levels to the word lines that the globalword line driver applies to the word lines.

The use of local word line drivers can improve the switching speed ofword lines and prior art designs generally include at least one PMOStransistor and at least one NMOS transistor in each local word linedriver. Use of PMOS transistors allows for the local word line voltageto be the same as the global word line voltage using lower phasevoltages than for NMOS-only local word line drivers due to the thresholdvoltages of NMOS transistors. However, while NMOS transistors used inthe local word line drivers can be fabricated in the same p-typesubstrate as the access transistors for the memory cells, the PMOStransistors used in the local word drivers can require the fabricationof an n-well in the p-type substrate to provide the n-type material forthe fabrication of the PMOS transistors. Forming a n-well for each ofthe local word line drivers can greatly increase the area of asemiconductor substrate used for fabricating the local word linedrivers, thereby potentially either increasing the cost or reducing thecapacity of the memory devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is block diagram of an embodiment of a memory system inaccordance with the present disclosure.

FIG. 2 is a block diagram of a portion of a memory bank array that canbe used in the memory system of FIG. 1.

FIG. 3A is a schematic of an embodiment of a main word line driver inaccordance with the present disclosure.

FIG. 3B is a signal timing diagram of the main word line driver of FIG.3A.

FIG. 3C is a schematic of an embodiment of a RF driver with optional rowhammer stress mitigation in accordance with the present disclosure forthe main word line driver of FIG. 3A.

FIG. 3D is flow diagram for managing operation of a main word linedriver in accordance with the present disclosure.

FIG. 4A is a schematic of an embodiment of an array of main word linedrivers in accordance with the present disclosure.

FIG. 4B is a schematic of an embodiment of an array of sub-word linedrivers in accordance with the present disclosure.

FIG. 5A is a schematic of another embodiment of an array of sub-wordline drivers in accordance with the present disclosure.

FIG. 5B is a signal timing diagram of a sub-word line driver of FIG. 5A.

FIG. 6 is a schematic of an embodiment of a FX phase driver inaccordance with the present disclosure.

FIG. 7 is flow diagram for managing operation of a sub-word line driverin accordance with the present disclosure.

DETAILED DESCRIPTION

As discussed in greater detail below, the technology disclosed hereinrelates to signal drivers for word line drivers and associated circuitsin memory systems and devices. A person skilled in the art, however,will understand that the technology may have additional embodiments andthat the technology may be practiced without several of the details ofthe embodiments described below with reference to FIGS. 1-6. In theillustrated embodiments below, the memory devices and systems areprimarily described in the context of devices incorporating DRAM storagemedia. Memory devices configured in accordance with other embodiments ofthe present technology, however, can include other types of memorydevices and systems incorporating other types of storage media,including PCM, SRAM, FRAM, RRAM, MRAM, read only memory (ROM), erasableprogrammable ROM (EPROM), electrically erasable programmable ROM(EEROM), ferroelectric, magnetoresistive, and other storage media,including non-volatile, flash (e.g., NAND and/or NOR) storage media.

FIG. 1 is a block diagram schematically illustrating a memory device 100in accordance with an embodiment of the present technology. The memorydevice 100 may include an array of memory cells, such as memory array150. The memory array 150 may include one or more banks MB (e.g., banksMB0 to MB15 in the example of FIG. 1), and each bank may include aplurality of word lines (WL), one or more bit lines (BL), and one ormore memory cells arranged at intersections of the word lines and thebit lines. The selection of a word line WL and the signal voltage on theword line WL can be performed by a row decoder 140 in combination withthe corresponding MWDs, SWDs, and FX phase drivers (“FX drivers,” “phasedrivers,” or “FXDs”). The MWDs, SWDs, and FXDs are discussed in furtherdetail below. The selection of a bit line BL can be performed by acolumn decoder 145. Sense amplifiers (SAMP) may be provided forcorresponding bit lines BL and connected to at least one respectivelocal I/O line pair (LIOT/B), which may in turn be coupled to at leastrespective one main I/O line pair (MIOT/B), via transfer gates (TG),which can function as switches.

The memory device 100 may employ a plurality of external terminals tocommunicate with an external memory controller and/or host processor(not shown). The external terminals can include command and addressterminals coupled to a command bus and an address bus to receive commandsignals CMD and address signals ADDR, respectively. The memory devicemay further include a chip select terminal to receive a chip selectsignal CS, clock terminals to receive clock signals CK and CKF, dataclock terminals to receive data clock signals WCK and WCKF, dataterminals DQ, RDQS, DBI, and DMI, power supply terminals VDD, VSS, VDDQ,and VSSQ.

The command terminals and address terminals may be supplied with anaddress signal and a bank address signal from an external memorycontroller and/or host processor. The address signal and the bankaddress signal supplied to the address terminals can be transferred, viaa command/address input circuit 105, to an address decoder 110. Theaddress decoder 110 can receive the address signals and supply a decodedrow address signal (XADD) to the row decoder 140, and a decoded columnaddress signal (YADD) to the column decoder 145. The address decoder 110can also receive the bank address signal (BADD) and supply the bankaddress signal to both the row decoder 140 and the column decoder 145.

The command and address terminals may be supplied with command signalsCMD, address signals ADDR, and chip selection signals CS, from a memorycontroller. The command signals may represent various memory commandsfrom the memory controller (e.g., including access commands, which caninclude read commands and write commands). The select signal CS may beused to select the memory device 100 to respond to commands andaddresses provided to the command and address terminals. When an activeCS signal is provided to the memory device 100, the commands andaddresses can be decoded and memory operations can be performed. Thecommand signals CMD can be provided as internal command signals ICMD toa command decoder 115 via the command/address input circuit 105. Thecommand decoder 115 can include a processor 116 and/or other circuits todecode the internal command signals ICMD to generate various internalsignals and commands for performing memory operations. For example, theprocessor 116 can execute the instructions to and/or other circuits canbe configured to generate row and column command signals and/or theassociated timing signals (e.g., in coordination with the timinggenerator 135) to select a word line and/or a bit line to perform thedesired memory operation. Of course, the processor/circuitry to generatethe command and/or timing signals can be located in another component ofthe memory device 100 such as, for example, address command inputcircuit 105 and/or an external controller/processor. The internalcommand signals can also include output and input activation commands,such as clocked command CMDCK.

When a read command is issued and a row address and a column address aretimely supplied with the read command, read data can be read from memorycells in the memory array 150 designated by these row address and columnaddress. The read command may be received by the command decoder 115,which can provide internal commands to input/output circuit 160 so thatread data can be output from the data terminals DQ, RDQS, DBI, and DMIvia read/write amplifiers 155 and the input/output circuit 160 accordingto the RDQS clock signals.

When a write command is issued and a row address and a column addressare timely supplied with the command, write data can be supplied to thedata terminals DQ, DBI, and DMI according to the WCK and WCKF clocksignals. The write command may be received by the command decoder 115,which can provide internal commands to the input/output circuit 160 sothat the write data can be received by data receivers in theinput/output circuit 160 and supplied via the input/output circuit 160and the read/write amplifiers 155 to the memory array 150. The writedata may be written in the memory cell designated by the row address andthe column address. The write data may be provided to the data terminalsat a time that is defined by write latency WL information. Operation ofthe I/O circuit 160 is known to those skilled in the art and thus, forbrevity, will not be discussed.

The power supply terminals may be supplied with power supply potentialsVDD and VSS. These power supply potentials VDD and VSS can be suppliedto an internal voltage generator circuit 170. The internal voltagegenerator circuit 170 can generate various internal potentials VPP, VOD,VARY, VPERI, VCC, VCCP, VCCP2, and the like based on the power supplypotentials VDD, VNWL, and VSS. The internal potential VPP can be used inthe row decoder 140, the internal potentials VOD and VARY can be used inthe sense amplifiers included in the memory array 150, and the internalpotential VPERI can be used in many other circuit blocks.

Clock input circuit 120 can receive external clock signal and generatevarious internal clock signals. For example, the clock input circuit 120can receive the external clock signals to generate internal clocksignals ICLK. The internal clock signals ICLK can be supplied to aninternal clock circuit 130. The internal clock circuit 130 can providevarious phase and frequency controlled internal clock signal based onthe received internal clock signals ICLK and a clock enable signal CKEfrom the command/address input circuit 105. For example, the internalclock circuit 130 can include a clock path (not shown in FIG. 1) thatreceives the internal clock signal ICLK and provides various clocksignals to the command decoder 115. The internal clock circuit 130 canfurther provide input/output (IO) clock signals. The IO clock signalscan be supplied to the input/output circuit 160 and can be used as atiming signal for determining an output timing of read data and theinput timing of write data. The IO clock signals can be provided atmultiple clock frequencies so that data can be output from and input tothe memory device 100 at different data rates. A higher clock frequencymay be desirable when high memory speed is desired. A lower clockfrequency may be desirable when lower power consumption is desired. Theinternal clock signals ICLK can also be supplied to a timing generator135 and thus various internal clock signals can be generated.

FIG. 2 illustrates a simplified block diagram of an exemplary structureof a memory bank MB of the memory array 150. As shown in FIG. 2, eachmemory bank MB can include one or more memory array sections SECT (e.g.,SECT0 to SECTn) having a group of memory cells. Each memory arraysection SECT includes an MWD (e.g., MWD0 to MWDn) which outputs theappropriate signal voltage on the corresponding global word line GR(e.g., GR0 to GRn). For example, when in an active or high state, theMWD can output a voltage level on the global word line GR that is at Vcc(e.g., in a range from about 2.3 volts to 2.7 volts such as, forexample, 2.5 volts), at Vccp (e.g., in a range from about 3.0 volts to3.5 volts such as, for example, 3.2 volts), or at some other voltagelevel corresponding to an active or high state. When in a pre-charge orstandby state, the MWD can output a voltage level on the global wordline GR that is at Vss (e.g., ground or 0 volts), at Vnwl (e.g., in arange from about −0.1 volts−0.25 volts such as, for example, −0.2volts), or at some other voltage level corresponding to a pre-charge orstandby state. When row hammer stress mitigation is enabled, during thetransition from the active or high state to the pre-charge or standbystate, the MWD can output an intermediate voltage level on the globalword line GR that is at Voff (e.g., 0.25 volts to 0.75 volts such as,for example, 0.5 volts). While the global word line GR can be directlycoupled to the memory cells in the memory bank MB, the global word lineGR extending through the memory bank MB can have substantial capacitanceand resistance, as discussed above. The capacitance and resistance canreduce the speed at which each MWD drives the respective global wordline GR. To mitigate this problem, each global word line GR can becoupled to one or more SWDs. For example, in some embodiments, eachglobal word line can connect to eight SWDs, sixteen SWDs, or some otherdesired number of SWDs. The SWDs can be fabricated between at least someof the memory cell arrays in memory bank MB. Each SWD outputs theappropriate signal voltage on the corresponding local word line WL(e.g., WL0 to WLn). For example, when in an active or high state, theSWD can output a voltage level on the local word line WL that is at Vcc(e.g., in a range from about 2.3 volts to 2.7 volts such as, forexample, 2.5 volts), at Vccp (e.g., in a range from about 3.0 volts to3.5 volts such as, for example, 3.2 volts), or at some other voltagelevel corresponding to an active or high state. When in a pre-charge orstandby state, the SWD can output a voltage level on the local word lineWL that is at Vss (e.g., ground or 0 volts), at Vnwl (e.g., in a rangefrom about −0.1 volts-0.25 volts such as, for example, −0.2 volts), orat some other voltage level corresponding to a pre-charge or standbystate. When row hammer stress mitigation is enabled, during thetransition from the active or high state to the pre-charge or standbystate, the SWD can output an intermediate voltage level on the localword line WL that is at Voff (e.g., 0.25 volts to 0.75 volts such as,for example, 0.5 volts). Depending on the type of SWD circuit, the highsignal voltage value on the local word line WL can be the same as thatof the global word line GR or lower than that of the global word line GRby a transistor threshold voltage Vt.

Each memory bank MB includes one or more FXDs that provide phase signalsPH and PHF, which are used to select the SWD based on decoded rowaddress signals and timing control signals. As seen in FIG. 2, the PHand/or PHF signals can be provided to a SWD in one or more sectionsSECT0-SECTn for selecting the appropriate SWD. For example, in someembodiments, each set of PH/PHF signals from a FXD can be connected to aSWD in each of a predetermined number of sections in sections SECT0 toSECTn. The predetermined number of sections can be seven sections, andthe set of PH/PHF signals can be connected to a SWD in each of the sevensections. However, in other exemplary embodiments, the predeterminednumber can be more than seven sections or less than seven sections. TheFXD is discussed in greater detail below.

FIG. 3A illustrates an exemplary embodiment of a main word line driver300. The MWD 300 can include a transistor 302 of a first type, such as,for example, a PMOS transistor, having a source coupled to a signalARMW. The voltage of signal ARMW and its complement ARMWF can correspondto a decoded address signal such as, for example, the first portion of adecoded row address. For example, the decoded row address ARMW (ARMWF)can correspond to one or more MWDs of a memory bank MB. The drain of thetransistor 302 can be connected to a drain of transistor 304 that can bedifferent from the first type, such as, for example a NMOS transistor.The interconnected drains of the transistors 302, 304 are coupled to aglobal word line GR. The source of transistor 304 can be connected to avoltage source that can be, for example, in a range of −0.25 volts to 0volts. For example, as seen in FIG. 3A, the voltage source is at Vnwl.However, in other embodiments, the voltage source can be at Vss or atsome other low voltage value. The gate of the transistor 304 can beconnected to the ARMWF signal. The gate of the transistor 302 is drivenby the RFF signal. The RFF and RF signals can correspond to a portion ofa decoded row address that can relate to, for example, one or more MWDsof a memory bank MB.

In addition to transistors 302 and 304, the MWD 300 can includeseries-connected transistors 306 and 308, which can be, for example,NMOS transistors. The drain of transistor 306 can be connected to globalword line GR and the source of transistor 306 can be connected to thedrain of transistor 308. The gate of transistor 306 can be connected tothe decoded address signal ARMW, and the gate of transistor 308 can beconnected to the RFF signal. The source of transistor 308 can beconnected to the RF signal. Based on the voltage values (high or low)for the ARMW, ARMWF, RF, and/or RFF signals, the MWD sets thecorresponding global word line GR to an active state or a pre-charge orstandby state. As discussed above, an active state or high state for theglobal word line GR can be at Vcc, at Vccp, or at other voltage levelcorresponding to an active or high state, and the pre-charge or standbystate for the global word line GR can be at Vss, at Vnwl, or at someother voltage level corresponding to a pre-charge or standby state. Thehigh state for the ARMW, ARMWF, RF, and RFF signals can be, for example,a voltage in a range of 2.3 volts to 3.5 volts, and the low state can bea voltage in a range of −0.25 volts to 0 volts (ground). For example,when in the high state, the ARMW, ARMWF, RF, and RFF signals can be at avoltage level corresponding to Vcc (e.g., in a range from about 2.3volts to 2.7 volts such as, for example, 2.5 volts), to Vccp (e.g., in arange from about 3.0 volts to 3.5 volts such as, for example, 3.2volts), or to some other voltage level corresponding to a high state ofthe signals. When in low state, the ARMW, ARMWF, RF, and RFF signals canbe at a voltage level corresponding to Vss (e.g., ground or 0 volts), toVnwl (e.g., in a range from about −0.1 volts-0.25 volts such as, forexample, −0.2 volts), or to some other voltage level corresponding tolow state.

The value of the high state is not necessarily the same for all thesignals. For example, one or more of the signals can have a high stateat 3.2 volts while one or more of the remaining signals have a highstate at 2.5 volts (or some other appropriate high voltage value).Similarly, the value of the low state is not necessarily the same forall the signals. For example, one or more of the signals can have a lowstate at −0.2 volts while one or more remaining signals have a low stateat 0 volts (or some other appropriate low voltage value). In someembodiments, the high state can be based on a high voltage source suchas, for example, Vcc, Vccp, or some other high voltage source, and thelow state can be based on a low voltage source such as, for example,Vss, vnwl, or some other low voltage source. In some embodiments, one ormore signals (e.g., the RF signal) and/or the global word line GR can beset to an intermediate voltage state Voff to mitigate the effects of rowhammer stress.

In operation, the MWD 300 receives the ARMW, ARMWF, RF, and RFF signalsand then sets the state of the global word line GR based the value ofthe signals. The processor 116 (and/or another processor) can controlthe decoded row address signals ARMW/ARMWF and RF/RFF to operate the MWD300. The circuits (not shown) to generate the ARMW and ARMWF signals areknown in the art and thus, for brevity, will not be discussed further.An exemplary RF driver circuit to generate the RF and RFF signals (alsoreferred to herein as “row factor” signals) in accordance with anembodiment of the present disclosure is shown in FIG. 3C. The MWD 300can include a pull-up circuit 301, a pull-down circuit 304 and anintermediate voltage circuit 305. The pull-up circuit 302 can include aPMOS transistor 302. The source of the PMOS transistor 302 can beconnected to the decoded address signal ARMW and the gate of the PMOStransistor 302 can be connected to the row factor signal RFF. The drainof the PMOS transistor can be connected to global word line GR. Thepull-down circuit 303 can include a NMOS transistor 304. The drain ofthe NMOS transistor 304 can be connected to the global word line GR andthe gate of the NMOS transistor 304 can be connected to decoded addresssignal ARMWF. The source of the NMOS 304 can be connected to a lowvoltage source, such as, for example, Vnwl (or, e.g., Vss or another lowvoltage source). The MWD 300 can also include an intermediate voltagecircuit 305. The intermediate voltage circuit 305 includes a NMOStransistor 306 connected in series with a NOMS transistor 308. The drainof the NMOS transistor 306 can be connected to the global word line GRand the gate of the NMOS transistor can be connected to decoded addresssignal ARMW. The source of the NMOS transistor 306 can be connected tothe drain of the NMOS transistor 308. The gate of the NMOS transistor308 can be connected to row factor signal RFF and the source of the NMOStransistor 308 can be connected to row factor signal RF. As discussedbelow, the intermediate voltage circuit 305 allows for the voltage onthe global word line GR to be pulled down to an intermediate voltagebetween the active voltage state and the pre-charge voltage state forrow hammer stress mitigation. Of course, in some embodiments, thefunctions of the pull-down circuit 304 and the intermediate voltagecircuit 305 can be incorporated into a single circuit.

With reference to FIGS. 3A and 3B, the MWD 300 can be configured so thatthe global word line GR is set at the active or high state if the ARMWsignal is at a high state and the RFF signal is at a low state (seesignals at t0). With the RFF signal in the low state and the ARMW signalin the high state, the transistor 302 will be ON to pull up the globalword line GR to the value of the ARMW signal, which can be at Vcc, atVccp, or at some other appropriate high voltage value. With the RFFsignal in the low state, the transistor 308 will be OFF to isolate theglobal word line GR from the value of the RF signal. Those skilled inthe art understand that “isolate” as used herein means a practicalisolation between the source and drain of a transistor and does notnecessarily mean a total electrical isolation as some leakage current inthe transistor can exist in some circumstances. In addition, with theARMWF signal at the low state, transistor 304 will be OFF to isolate theglobal word line GR from the voltage source Vnwl (or, e.g., Vss or someother low voltage source).

In some embodiments, when transitioning from the active or high state tothe pre-charge or standby state, the MWD 300 enters an intermediatevoltage state (or row hammer stress mitigation state) prior to enteringthe pre-charge or standby state. For example, at time t1, when the RFFsignal is set to a high state, the RF signal is set to an intermediatestate having a voltage Voff for a predetermined period of time (e.g.,from time t1 to t2). In some embodiments, Voff can be a value in a rangeof 0.25 volts to 0.75 volts such as, for example, 0.5 volts. Turning toFIG. 3A, with the RFF and ARMW signals set at a high state, thetransistors 306 and 308 are ON to pull down the value of the global wordline GR to the value of the RF signal, which is at Voff. In addition,with the RFF signal in a high state, the transistor 302 is OFF toisolate the value of the ARMW signal from the global word line GR. Thus,in this embodiment, the global word line GR transitions from an activeor high state to an intermediate voltage Voff prior to transitioning toa pre-charge or standby state at time t2. By limiting the step change involtage when going from the active or high state to the pre-charge orstandby state, adjacent word lines WL in the memory bank MB do notexperience the effects of a rapid change in voltage levels and rowhammer stress can be mitigated. In some embodiments when row hammerstress mitigation is not required or desired, the RF signal is not setto Voff and the global word line GR transitions from the active or highstate to the pre-charge or stand by state without going to anintermediate voltage first (see, for example, the dotted line in FIG.3B).

In some embodiments, at either time t1 (no row hammer stress mitigation)or time t2 (with row hammer stress mitigation), the ARMWF signal can beset to a high state to turn ON the transistor 304 to connect the globalword line GR to Vnwl (or, e.g., Vss or some other low voltage source).With ARMW now at a low state, transistor 306 will be OFF to isolate theRF signal from the global word line GR. In addition, the value of theRFF signal is at a high state to ensure transistor 302 is OFF to isolatethe global word line GR from the ARMW signal. Table 1 provides a logictable illustrating the state (A—active, P—pre-charge, or I—intermediatevoltage (row hammer stress mitigation) of the global word line GR basedon the state of the decoded address signals and row factor signals forMWD 300.

TABLE 1 ARMW ARMWF RFF RF GR L H H L P H L L H A H L H I I

FIG. 3C is a schematic of an exemplary embodiment of a row factor drivercircuit (“RF driver circuit”) with row hammer stress mitigation. As seenin FIG. 3C, the RFF and RF signals used by the MWD 300 can be generatedby RF driver circuit 310. The RF driver circuit 310 can receive inputsignals RMSMWP, RFX_n, and RMSXDP, which are decoded row address and/ortiming signals from a row decoder (not shown). For example, the RFX_nsignal can be a decoded address signal that corresponds to a memory bankand/or one or more MWDs of the memory bank, where X can represent amemory bank and n can represent the corresponding one or more MWDswithin the memory bank. The RMSMWP and RMSXDP signals can be timingsignals for generating the RFF and RF signals used in the operation ofthe corresponding one or more MWDs.

Prior to time t0 (see FIG. 3B), the RFX_n signal can be set at a lowstate, which can mean that the pertinent memory bank and/or thecorresponding one or more MWDs are not selected for operation. That is,with the RFX_n signal at the low state, the output of NAND gate circuit312 and thus the RFF signal is high to isolate the global word line GRfrom the ARMW signal. In addition, a low RFX_n signal means that theoutput of NAND gate circuit 316 is also high. With a high output on theNAND gate circuit 316, NMOS transistor 332 is ON. Because NMOStransistor 330 is a continuously gated transistor, the node 321 and thusthe RF signal is pulled down to the value of Vnwl (or, e.g., Vss, orsome other low voltage source) via the transistor 332. Thus, prior tot0, the RFF and RF signals to the MWD 300 will be high and low,respectively.

In addition, with a low RFX_n signal, the output of AND gate circuit 314is low and NMOS transistor 322 is OFF, which isolates voltage Voff (usedin row hammer stress mitigation) from node 321 even though the NMOStransistor 326 is ON due to the high RFF signal. Similarly, the PMOStransistor 320 is OFF to isolate the voltage V1 from the node 321. ThePMOS transistor 320 is OFF because the source voltage V1, in someembodiments, is set to be lower than the high voltage value of the RFFsignal. For example, if the high voltage value of the RFF is at Vccp,then the voltage V1 can be Vccp−Vt, where Vt is the threshold voltage ofthe transistor 320 (e.g., if Vccp=3.2 volts and Vt is 0.7 volts, then V1is 2.5 volts). The voltage V1 can be set to be below the high voltagevalue of the RFF signal by at least the threshold voltage of thetransistor 320 in order to prevent unreliable operation of thetransistor 320.

The RFX_n signal can be set to high state (e.g., corresponding to timet0 in FIG. 3B) to select the pertinent memory bank and/or thecorresponding one or more MWDs for operation. In some embodiments, whenRFX_n is in the high state, the timing signals RMSWMP and RMSXDP arealso set to the high state. With the RFX_n and RMSWMP signals at thehigh state, the output of NAND gate circuit 312 is low, which means theRFF signal is low. A low signal value on RFF means that the ARMW signalis connected to the global word line GR in MWD 300. In addition, a lowsignal value on RFF means that NMOS transistor 326 is OFF to isolateVoff from node 321. With RFF low, PMOS transistor 320 is turned ON topull up node 321 and thus the RF signal high to the voltage V1. In someembodiments, V1 can be 2.5 volts and the RF signal can be pulled up to avalue of 2.5 volts. With the RFX_n and RMSXDP signals at the high state,the NMOS transistor 322 is ON but because NMOS transistor 326 is OFF,the node 321 remains isolated from the voltage source Voff. To preventunreliable operation, a continuously gated NMOS transistor 324 isprovided in series between NMOS transistor 322 and NMOS transistor 326.The NMOS transistor 324 has a gate voltage Von that is sufficient tokeep transistor 324 continuously gated. The inclusion of continuouslygated transistor 324 provides more reliability to the RF driver circuit310 by providing a resistive path for the leakage current going throughNMOS transistor 326 to create a voltage drop in the leakage current pathwhen the NMOS transistor 326 is OFF.

With the RFX_n and RMSXDP signals at the high state, the output of NANDgate circuit 316 is low, which means that NMOS transistor 332 is OFF toisolate node 321 from the voltage source Vnwl (or e.g., Vss or someother low voltage source). To prevent unreliable operation, acontinuously gated NMOS transistor 330 is provided in series betweennode 321 and the NMOS transistor 332. The signal at the gate oftransistor 330 can be at a voltage Vccp (as shown in FIG. 3C), at Vcc,or at some other appropriate voltage to keep transistor 330 ON.Continuously gated NMOS transistor 330 provides more reliability to theRF driver circuit 310 by providing a resistive path for the leakagecurrent going through NMOS transistor 332 to create a voltage drop inthe leakage current path when the NMOS transistor 332 is OFF.

After a predetermined time period (e.g., at time t1 see FIG. 3B.), thetiming signal RMSMWP can be set at a low state, which sets the output ofNAND gate circuit 312 and thus the RFF signal at a high state. With theRFF signal at the high state, the ARMW signal is isolated from theglobal word line GR. With the RFF signal at a high state PMOS transistor320 is off to isolate the node 321 from the voltage source V1 and theNMOS transistor 326 is turned on.

In some embodiments, when row hammer stress mitigation is desired, theRMSXDP signal remains high for a predetermined period (e.g., from timet1 to t2, see FIG. 3B) to allow for a “soft landing” for the RF voltageand thus the global word line voltage GR. As discussed below, a “softlanding” on the global word line GR also means a “soft landing” on thelocal word line WL to mitigate the row hammer stress between adjacentlocal word lines WL in a memory bank MB. To mitigate the row hammerstress, the global word line GR is stepped down to an intermediatevoltage Voff prior to entering the pre-charge or standby state. This isaccomplished by having the global word line GR follow the RF signal fora predetermined time period (e.g., between t1 and t2, see FIG. 3B). Forexample, with the RMSXDP and RFX_n signals in the high state, the outputof AND gate circuit 314 remains at a high state to keep NMOS transistor322 ON. With NMOS transistors 322, 324, and 326 all ON, the node 321 andthus the RF signal is pulled down to the voltage Voff, which can be, forexample, 0.5 volts. The predetermined period that the RMSXDP signalremains high after the RMSMWP signal is set at a low state cancorrespond to the time period between t1 and t2. In some embodiments,when no row hammer stress mitigation is desired, the RMSXDP signal canbe set to a low state at the same time the RMSMWP signal is set at a lowstate. When the RMSXDP signal is set to a low state, the output of ANDgate circuit 314 is set low to isolate the node 321 from the voltageVoff. In addition, the output of NAND gate circuit 316 is set high toturn ON NMOS transistor 332 to pull down the node 321 to the voltageVnwl (or e.g., Vss or some other low voltage source). As discussedabove, the RFF and RF signals generated by the RF driver 310 incoordination with the ARMW and ARMWF signals can be used by MWD 300 toset the global word line voltage.

FIG. 3D is a flow diagram illustrating example method 350 for managingthe operation of the MWDs. The method 350 can be performed by processinglogic that can include hardware (e.g., processing device, circuitry,dedicated logic, programmable logic, microcode, hardware of a device,integrated circuit, etc.), software (e.g., instructions run or executedon a processing device), or a combination thereof. In some embodiments,the method 350 is performed by the processor 116 and/or anotherprocesser or processors that are external and/or internal to memorydevice 100. Although shown in a particular sequence or order, unlessotherwise specified, the order of the processes can be modified. Thus,the illustrated embodiments should be understood only as examples, andthe illustrated processes can be performed in a different order, andsome processes can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At block 360, the processing device (e.g., processor 116 and/or anotherprocessor) generates a first row factor signal and a second row factorsignal in a memory device. In some embodiments, as discussed above, thefirst row factor signal can be the RFF signal and the second row factorsignal can be the RF signal which are generated by a RF driver circuit(e.g., RF driver circuit 310). At block 370, the processing device(e.g., processor 116 and/or another processor) drives a global word lineof the memory device to an active state by setting the first row factorsignal to a first value when a first decoded address signal is at a highstate. For example, the global word line can be local word line GR(e.g., GR0 to GRn) that is generated by a MWD. In some embodiments, forexample as seen in FIGS. 3A and 3B, the global word line GR can go to anactive or high state if the decoded address signal ARMW is at a highstate (e.g., Vccp) and the pull-up transistor 312 is ON due to the RFFsignal being at a low state. At block 380, the processing device (e.g.,processor 116 and/or another processor) drives the global word line tofollow a value of the second row factor signal by setting the first rowfactor signal to a second state while the first decoded address signalis at the high state. For example, in some embodiments as seen in FIGS.3A and 3B, the global word line GR goes to an intermediate value Voff ofthe RF signal. This scenario occurs when the decoded address signal isat the high state (e.g., Vccp), which turns ON transistor 306, and theRFF row factor signal is at a high state (e.g. Vccp), which turns ONtransistor 308 and turns OFF transistor 302. The intermediate voltagecorresponds to the row hammer stress mitigation state, as discussedabove.

FIG. 4A illustrates an exemplary arrangement of a portion of an MWDarray in a memory bank MB. For simplicity, FIG. 4A illustrates only fourglobal word lines GR0, GR1, GR2, and GR3 and the respective MWDs 410,420, 430, and 440. Of course, a memory bank MB can have more than fourglobal word lines, including their corresponding MWDs, and those skilledin the art would understand how to apply the present disclosure to anydesired number of MWDs. In addition, because those skilled in the artunderstand that the configuration and operation of the MWDs 410, 420,430, and 440 are similar to that of MWD 300, the configuration andoperation will not be repeated. As shown in FIG. 4A, the state of eachMWD is determined by two sets of decoded row address signalsARMWn/ARMWnF and two sets of decoded row address signals RFm<n>/RFmF<n>.The processor 116 (and/or another processor) can control the two sets ofdecoded row address signals ARMWn/ARMWnF and two sets of decoded rowaddress signals RFm<n>/RFmF<n> to operate the MWDs 410-440. The ARMWnsignal and its complement ARMWnF signal can be received by one or moreMWDs and n identifies the group of MWDs that receive the same ARMW andARMWF signals. The memory bank MB can have one or more groups n (e.g.,for a memory bank having 16 groups that are designated by n0 to n15).For brevity and clarity, in the exemplary embodiment of FIG. 4A, thenumber of groups n is two, designated 0 and 1, and the number of MWDs ineach group is two. For example, in the embodiment of FIG. 4A, thedecoded row address signals ARMW0/ARMW0F are received by MWDs 410 and430, and the decoded row address signals ARMW1/ARMW1F are received byMWDs 420 and 440. Similarly, the RFmF<x> signal and its complementRFm<x> signal can be received by one or more MWDs where x identifies thegroup of MWDs that receive the same RFF and RF signals. For example, inthe example of FIG. 4A, the decoded row address signals RFmF<0>/RFm<0>are received by MWDs 410 and 420, and the decoded row address signalsRFmF<1>/RFm<1> are received by MWDs 430 and 440. The m can correspond tothe memory bank, which is identified as 3 in the exemplary embodiment ofFIG. 4A. The combination of the ARMWn/ARMWnF signals and theRFm<x>/RFmF<x> signals selects the appropriate state (active or highstate or pre-charge or standby state) for each MWD in memory bank MB.For example, in the exemplary embodiment of FIG. 4A, the signals ARMW0and ARMW1F are set at a high state (e.g., both at 3.2 volts), and ARMW1and ARMW0F are set at a low state (e.g., −0.2 volts and 0 volts,respectively). In addition, the RF3<0> and RF3F<1> signals are set at ahigh state (e.g., 2.5 volts and 3.2 volts respectively), and RF3F<0> andRF3<1> are set at a low state (e.g., both at −0.2 volts). As seen inFIG. 4A, the circles around transistors indicate which transistors areON to allow the source voltage to pass through. The resulting globalword line signal values for GR0, GR1, GR2, and GR3 are 3.2 volts (activeor high state), −0.2 volts (pre-charge or stand-by state), −0.2 volts(pre-charge or stand-by state), and −0.2 volts (pre-charge or stand-bystate), respectively. The global word line signals (e.g., the signals onglobal word lines GR0 to GR3) can then be sent to respective SWDs, whichdrive memory cells based on decoded row address signals as discussedbelow. Table 2 provides a logic table illustrating the state (A—activestate, P—pre-charge state, I—Intermediate voltage (e.g., row hammerstress mitigation) state) of the global word lines GR0-GR3 for therespective MWDs 410 to 440.

TABLE 2 ARMW0 ARMW0F ARMW1 ARMW1F RF3F<0> RF3<0> RF3F<1> RF3<1> GR0 GR1GR2 GR3 H L L H L H H L A P P P H L L H H I H L I P P P H L L H H L L HP A P P H L L H H L H I P I P P L H H L L H H L P P A P L H H L H I H LP P I P L H H L H L L H P P P A L H H L H L H I P P P I

As discussed above, each of the global word lines (e.g., GR0 to GR3)connects to SWDs in order to quickly drive the signal levels on therespective word lines. FIG. 4B illustrates exemplary embodiment of a SWDarray arrangement corresponding to global word lines GR0 and GR1. Forclarity, only two sets of SWDs are shown for each global word line GR.For example, SWDs 450 and 460 are connected to global word line GR0, andSWDs 470 and 480 are connected to global word line GR1. However, morethan two SWDs can be connected to each global word line GR such as, forexample eight SWDs, sixteen SWDs or more. Each of the SWDs 450, 460,470, and 480 output a local word line WR0, WR1, WR2, and WR3,respectively. As seen in FIG. 4B, the configuration of each of the SWDs450, 460, 470, and 480 can be the same. Accordingly, for brevity, onlythe configuration and operation of SWD 450 will be discussed.

SWD 450 can include a pull-up circuit having a PMOS transistor 452 thatturns ON when the PHF phase signal connected to the gate of the PMOStransistor 452 is low (e.g., at Vnwl, Vss, or another low value). TheSWD 450 can also include a NMOS transistor 456 that is placed inparallel with the PMOS transistor 452. The NMOS transistor 456 can actas a pull-up or pull-down circuit based on the voltage on the globalword line GR0 and is turned ON when the PH phase signal connected to thegate of the NMOS transistor 456 is high (e.g., Vccp, Vcc, or anotherhigh voltage value). The SWD 450 can also include a pull-down circuithaving a NMOS transistor 454 and is turned ON when the PHF phase signalconnected to the gate of the NMOS transistor 454 is high (e.g., Vccp,Vcc, or another high voltage value). The sources of transistors 452 and456 can be connected to the global word line GR0, and the drains of thetransistors 452 and 456 can be connected to a drain of the transistor454. The interconnected drains of the transistors 452, 456 and 454 arecoupled to a local word line WL0. The source of transistor 454 can beconnected to a low voltage source that is in a range of −0.2 volts to 0volts. For example, the source of transistor 454 can be Vnwl as shown inFIG. 4B. In some embodiments, the low voltage source can be Vss or someother low voltage source.

As shown in FIG. 4B, the selection of the SWD and thus the local wordline WL for accessing the appropriate memory cell is determined by thePHn/PHFn signals (also referred to herein as phase signals)corresponding to decoded row address signals, where n is 0 or 1 in theexemplary embodiment of FIG. 4B. The PHn and PHFn phase signals can beconnected to one or more SWDs. For example, in FIG. 4B, each set ofphase signals (e.g., PH0/PHF0 and PH1/PHF1) are shown connected to twoSWDs (e.g., 450/470 and 460/480, respectively). However, the set ofphase signals can be connected to more than two SWDs. For example, insome embodiments, each set of PH/PHF signals can connect to an SWD ineach section SECT of a predetermined number of sections in sectionsSECT0 to SECTn (see FIG. 2). For example, the predetermined number ofsections can be seven sections, and the set of PH/PHF signals can beconnected to a SWD in each of the seven sections. However, in otherexemplary embodiments, the predetermined number can be more than sevensections or less than seven sections. In some conventional SWDs theglobal word line signals are used in switching the transistors in theSWD (e.g., the complement of the GR0 signal can be connected to the gateof the pull-up PMOS transistor in some conventional transistor and thePH phase signal can be connected to the source of the pull-up PMOStransistor). However, by using the PH and PHF phase signals to switchthe transistor gates of a SWD and connecting the set of PH/PHF phasesignals to an SWD in one or more sections SECT0 to SECTn, the layoutarea on the memory device 100 needed for the phase drives can bereduced.

As seen in FIG. 4B, the global word line GR0 signal is provided by theMWD (e.g., MWD 410) as discussed above. The PH0 and PHF0 phase signalscan be set to appropriate states by a phase driver, which is known tothose skilled in the art, to place the SWD 450 in the active state,intermediate voltage state, and the pre-charge state. For example, asseen in FIG. 4B, the PH0 phase signal can be set at a high state havinga value of Vccp, which can be in a range of 3.0 volts to 3.5 volts. Insome embodiments, the value of Vccp can be in a range of 3.2 volts. Insome embodiments, the high state can be Vcc. The PHF0 phase signal canbe set at a low state having a value of, for example, Vnwl (or e.g., Vssor another low voltage value). With PH0 at a high state, SWD 450 isselected to be in an active state to receive and follow the value of theglobal word line GR0, and the memory cells attached WL0 can be accessedfor memory operations (e.g., read, write, etc.) based on the value ofthe global word line GR0. As discussed above, in some embodiments, theMWD will set the global word line GR to an intermediate voltage statewhen transitioning from the active state to the pre-charge state. Forexample, as seen in FIG. 4B, the global word line GR0 can have a valueof Vccp for the active state and a value of Voff for the intermediatestate. With PHF0 low and PH0 high, the SWD 450 will set the local wordline WL0 to follow the voltage on the global word line GR0, includingthe intermediate voltage stage (e.g., having a voltage Voff) during thetransition from the active stage (e.g., Vccp, Vcc) to the pre-chargestate (e.g., Vnwl, Vss). With the global word line at a low state, thePHF1 phase signal at a high state, and the PH1 phase signal at a lowstate, the other SWDs 460, 470, 480 can be in a pre-charge state (e.g.,Vnwl, Vss). As seen in FIG. 4B, the circles around transistors indicatewhich transistors are ON to allow the source voltage to pass through inthe respective SWDs.

FIG. 5A illustrates another exemplary embodiment of a SWD arrayarrangement corresponding to global word lines GR0 and GR1. For clarity,only two sets of SWDs are shown for each global word line GR. Forexample, SWDs 510 and 520 are connected to global word line GR0, andSWDs 530 and 540 are connected to global word line GR1. However, morethan two SWDs can be connected to each global word line GR. Each of theSWDs 510, 520, 530, and 540 output a local word line WL0, WL1, WL2, andWL3, respectively. As seen in FIG. 5A, the configuration of each of theSWDs 510, 520, 530, and 540 can be the same. In some embodiments, eachSWD can exclusively use NMOS transistors for driving the local word lineWL. That is the SWD is an NMOS-only SWD. For example, SWD 510 caninclude an NMOS transistors 512, which acts as pull-up circuit, and anNMOS transistors 514, which acts as a pull-down circuit. The drain ofthe transistor 512 can be connected to a drain of the transistor 514.The interconnected drains of the transistors 512, 514 are coupled to alocal word line WL0. The source of transistor 512 can be connected tothe corresponding global word line GR0, and the source of transistor 514can be connected to a low voltage source that is in a range of −0.2volts to 0 volts. For example, the source of transistor 514 can be Vnwlas shown in FIG. 5A. In some embodiments, the low voltage source can beVss or some other low voltage source. As shown in FIG. 5A, the selectionof the SWD and thus the word line WL for accessing the appropriatememory cell is determined by the PHn/PHFn signals corresponding todecoded row address signals, where n is 0 or 1 in the exemplaryembodiment of FIG. 5A. As discussed above, each set of PHn/PHFn phasesignals can be connected to a SWD in a predetermined number of sectionsin sections SECT0 to SECTn.

The timing control of NMOS transistors such as those used in, forexample, SWDs 510-540 can create issues related to the stability andreliability of the NMOS transistors. For example, the stability andreliability and reliability of the NMOS transistors can be affected ifthe NMOS transistors are switched when there is a high source to drainvoltage (Vsd) or drain to source voltage (Vds). In exemplaryembodiments, of the present disclosure, the timing operation of one ormore of the NMOS transistors in the SWD and/or the signals to the SWDare controlled so that switching occurs at a minimum or reduced Vds orVsd magnitude.

FIG. 5B illustrates a timing diagram that provides stability andreliability for the operation of the NMOS-only SWDs of FIG. 5A. Forbrevity, only the timing for SWD 510 is shown, but those skilled in theart understand that the timing diagram for the other SWDs will besimilar. The global word line GR0 signal is provided by the MWD (e.g.,MWD 410) as discussed above. For example, the value of global word lineGR0 can be at Vccp (or another high voltage level), at Voff (or anotherintermediate voltage level), or at Vnwl (or another low voltage level).Prior to time T0, the PH0 phase signal can be set at a high state havinga value of Vccp2, which can be in a range of 3.8 volts to 4.7 volts. Insome embodiments, the value of Vccp2 can be in a range of 4.2 volts to4.5 volts, such as, for example, 4.2 volts or 4.5 volts. The PHF0 phasesignal can be set at a low state having a value of, for example, Vnwl(or e.g., Vss or another low voltage value). The PH0 and PHF0 phasesignals can be set to their respective states by an FX phase driver, seeFIG. 6, discussed below. With PH0 at a high state, SWD 510 is selectedto be in an active state to receive and follow the value of the globalword line GR0, and the memory cells attached WL0 can be accessed formemory operations (e.g., read, write, etc.) based on the value of theglobal word line GR0. The other SWDs 520, 530, 540 can be in apre-charge state.

Operation of the SWD 510 is provided with reference to FIGS. 5A and 5B.At time T0, the processor 116 (and/or another processor) can control theinput signals to a FX phase driver (e.g., FXD 600 discussed below) toset the PH0 phase signal to a high state (e.g., Vccp2) and the PHF0 to alow state (e.g., Vnwl). As seen in FIG. 5B, the setting of the PH0signal to the high state occurs when the global word line is at thepre-charge state such that Vds/Vsd at the time PH0 is at a minimummagnitude, which improves the reliability of SWD 510. After transistor512 is ON due to PH0 going to the high state, at time T1, the processor116 (and/or another processor) can control the input signals to MWD(e.g., MWD 300, 410-440, discussed above) to set the value of the globalword line GR0 to the active or high state. In some embodiments, thevalue of the global word line GR is Vccp, which can be, for example, 3.2volts. With the PHF0 phase signal at the low state, the NMOS transistor514 is OFF and the local word line WL0 is isolated from the voltagesource Vnwl (or, e.g., Vss or another low voltage source). With the PH0phase signal at the high state, the NMOS transistor 512 pulls up thelocal word line WL0 to the value Vccp (or another appropriate high statevalue) of the global word line GR0. In some embodiments, the high statevalue of the PH0 phase signal is higher than the active state value ofthe global word line GR0 by at least the threshold voltage of the NMOStransistor 512. For example, if the value of global word line GR0 is 3.2volts and the threshold value of transistor 512 is 0.6 volts, the PH0phase signal can be set at a value that 3.8 volts or greater. Forexample, the PH0 phase signal can be set at a value of Vccp2, which canbe in a range of 3.8 volts to 4.7 volts. In some embodiments, the valueof Vccp2 can be in a range of 4.2 volts to 4.5 volts, such as, forexample, 4.2 volts or 4.5 volts. By setting the value of the PH0 phasesignal at or higher than the value of the global word line GR0 plus thethreshold voltage of transistor 512 (e.g., Vccp+Vt), the value of thelocal word line WL0 can be pulled up to the full voltage of the GR0signal. In some embodiments, the PH0 voltage value is higher than thevalue of the global word line GR0 plus the threshold voltage oftransistor 512 (e.g., greater than Vccp+Vt). That is, the voltage of PH0is set higher than that the minimum needed for ensuring that the localword line WL0 is at the full voltage of the global word line GR0.However, a higher than minimum required voltage (e.g., greater thanVccp+Vt) can mean that the pull-up transistor in the NMOS-only SWD isless reliable.

Turning to FIG. 5B, at time T2, the processor 116 (and/or anotherprocessor) can control the input signals to MWD (e.g., MWD 300, 410-440,discussed above) to start the transition of the global word line GR0signal from the active or high state to a pre-charge or standby state(time T2 can correspond to time t1 in FIG. 3B). In some embodiments, ifrow hammer stress mitigation is desired, the value of global word lineGR0 signal is set to an intermediate voltage Voff as discussed above.Because the NMOS transistor 512 is still ON at this time, the value ofthe local word line WL0 signal will follow the global word line GR0signal and the local word line WL0 signal will be set to theintermediate voltage Voff. The voltage Voff is maintained for apredetermined time period T2 to T3, which can correspond to the timeperiod t1 to t2 in FIG. 3B, before dropping to the pre-charge or standbystate. By performing a “soft landing” from the active or high state tothe pre-charge or standby state on the local word line WL, row hammerstress on one or more of the adjacent local word lines (e.g., WL1 toWL3) on the memory bank MB is mitigated. In some embodiments, if rowhammer stress mitigation is not desired, at time T2, the processor 116(and/or another processor) can control the input signals to MWD (e.g.,MWD 300, 410-440, discussed above) to set the global word line GR0 tothe pre-charge state (see dotted line) having a value Vnwl (or e.g., Vssor some other low voltage value) and the local word line WL0 will followthe global word line GR0 (see dotted line).

After the global word line GR0 has reached the pre-charge state, at timeT4, the processor 116 (and/or another processor) can control the inputsignals to a FX phase driver (e.g., FXD 600 discussed below) to set thePH0 phase signal to a low state having a value Vnwl (or e.g., Vss orsome other low voltage value). At this time, the processor 116 (and/oranother processor) can control the input signals to a FX phase driver(e.g., FXD 600 discussed below) to set the PHF0 phase signal to a highstate having a value Vcc (e.g., 2.5 volts) or Vccp (e.g., 3.2 volts). Insome embodiments, the setting of the PHF0 phase signal to the high statecan be delayed such that both the PH0 and PHF0 phase signals are at alow value, which means that NMOS transistors 512 and 514 are both offand the local word line WL0 is isolated from both the high and lowvoltage sources. However, any delay in setting the PHF0 to the highstate after the PH0 is set to the low state should be limited since thelocal word line WL0 will be at a float value. With the PHF0 phase signalat the high state, the transistor 514 is turned on and the value of thelocal word line WL0 is pulled down to the value of the low voltagesource Vnwl (or, e.g., Vss or some other low voltage source). Theexemplary timing diagram as shown in FIG. 5B for the PH0 and PHF0 phasesignals improves the reliability of the NMOS transistor and thusNMOS-only SWD by ensuring that the NMOS transistors are switched atminimal or reduced Vds/Vsd magnitudes.

As discussed above, in some sub-word line drivers (e.g., see FIG. 4B), aPMOS transistor is included in each of the SWDs. The PMOS transistorallows for the word line WL to reach the full high voltage of the globalword line GR. For example, if a global word line (e.g., GR0, GR1, GR2,or GR3) is at 3.2 volts, the corresponding local word line (e.g., WL0,WL1, WL2, or WL3) can be pulled up the full 3.2 volts by a PMOStransistor. However, PMOS transistors can require an n-well in a p-wellfrom which the memory cell arrays are formed, thereby causing the layoutarea for the SWD to be larger. Due the large number of global word linesin a typical memory device, an NMOS-only SWD such as that shown in FIG.5A reduces the amount of space needed for the SWDs by avoiding the needfor an n-well for each of the SWDs, which reduces the area needed by theSWDs on a semiconductor substrate. However, by going to a NMOS-only SWD,full voltage at the local word line (e.g., WL0, WL1, WL2, WL3) may notbe achieved unless the gate voltage necessary to couple the voltage fromthe global word line (e.g., GR0, GR1, GR2, GR3) to the respective localword line (e.g., WL0, WL1, WL2, WL3) is increased by at least thethreshold voltage of the NMOS transistors. For example, the embodimentin FIG. 5A, as discussed above, a gate voltage of Vccp2 (e.g., 4.2volts, 4.5 volts) is applied by the PH0 phase signal instead of a gatevoltage of Vccp (e.g., 3.2 volts) used in conventional circuits. Thus,the voltage of the PHn phase signals applied to the gates of the pull-upNMOS transistors in NMOS-only SWDs can be at a higher voltage (e.g.,Vccp2) than that (e.g., Vcc, Vccp, etc.) used for the pull-up PMOStransistors in conventional SWDs. In some embodiments, Vccp2 can be in arange of 3.8 volts to 4.7 volts. In some embodiments, the value of Vccp2can be in a range of 4.2 volts to 4.5 volts, such as, for example, 4.2volts or 4.5 volts. Conventional FX phase drivers are not able toprovide such high PH phase signal voltages without experiencingstability and reliability issues.

In exemplary embodiments of the present disclosure, FX phase driversthat provide the PHn and PHFn phase signals are configured to reliablyprovide signal voltages that range from Vnwl to Vccp2 (e.g., −0.2 voltsto 4.7 volts). As seen in FIG. 6, FX driver 600 receives decoded rowaddress signal RF0 and timing control signals R1AC and R2ACF. Theprocessor 116 (and/or another processor) can control the decoded rowaddress signal RF0 and/or the timing control signals R1AC and R2ACF tooperate the FX phase driver 600. The circuits (not shown) to generatethe timing control signals and the decoded row address signals for FXdrivers are known in the art and thus, for brevity, will not bediscussed further. As seen in FIG. 6, the FXD 600 includes a phasecircuit 610 for generating a PHF phase signal and a phase circuit 620for generating a PH phase signal that is generally the complement of thePHF phase signal. The phase circuit 610 includes a pull-up circuit 611and a pull-down circuit 613. In some embodiments, the pull-up circuit611 can include a transistor 612 and a transistor 618 that are connectedin parallel. In some embodiments, the pull-down circuit 613 can includea transistor 614 and a transistor 616 that are connected in series. Thetransistor 612, which can be, for example, a PMOS transistor, can have adrain coupled to the drain of a transistor 614, which can be, forexample, a NMOS transistor. The source of transistor 612 is coupled to avoltage source, such as, for example, Vccp (or, e.g., Vcc or anotherhigh voltage source), and the source of transistor 614 is connected tothe drain of transistor 616, which can be a NMOS transistor. The sourceof transistor 616 is coupled to a voltage source, such as, for example,Vnwl (or, e.g., Vss or another low voltage source). As seen in FIG. 6,the interconnected drains of transistors 612 and 614 are coupled to aPHF signal line. In addition, transistor 618, which can be, for example,a PMOS transistor, is connected in parallel with transistor 612. Thus,the source of transistor 618 can be connected to the same voltage sourceas that of transistor 612, such as, for example, Vccp (or, e.g., Vcc oranother high voltage source), and the drain of transistor 618 can beconnected to the PHF signal line.

As seen in FIG. 6, the gates of the transistors 612 and 614 receive thedecoded row address signal RF0 and the gates of transistors 616 and 618receive the timing control signal R1AC. If the timing signal R1AC has alow value (e.g., 0 volts), the transistor 616 is OFF, which isolates thevoltage source Vnwl (or, e.g., Vss or another low voltage source) fromthe PHF signal line. In addition, the low value on timing control signalR1AC means that the PMOS transistor 618 is ON. With transistor 618 ON,the PHF signal line is pulled up to the source voltage, which in thiscase can be Vccp (or, e.g., Vcc or another high voltage source). As seenin FIG. 5A and as discussed above, with a PHF signal that is high, thecorresponding SWD is inactive and the SWD's word line has a low value,e.g., Vnwl (or, e.g., Vss or another low voltage source).

The PHF signal is transmitted to the circuit 620 for generation of thePH phase signal, which as discussed above selects the SWD to activate.The circuit 620 includes a pull-up circuit 621 and a pull-down circuit623. The pull-up circuit 621 can include a transistor 622 connected inseries to a transistor 624. The pull-down circuit 623 can include astabilization circuit 625 connected in series to transistors 630 and632, which are connected in parallel. The stabilization circuit 625 caninclude one or more continuously gated transistors. For example, as seenin FIG. 6, the stabilization circuit 625 includes two continuously gatedtransistors 626 and 628 that are connected in series.

The transistor 622, which can be a PMOS transistor, can have a drainconnected to the source of transistor 624, which can be a PMOStransistor. The source of transistor 622 can be connected to a voltagesource such as, for example, Vccp2. In some embodiments, as discussedabove, the value of Vccp2 can be higher than the active word linevoltage, which can be, for example, Vccp (or, e.g., Vcc or another highvoltage source). The drain of transistor 624 can be connected to thedrain of transistor 626, which can be a NMOS transistor. As seen in FIG.6, the interconnected drains of transistors 624 and 626 are coupled tothe PH signal line. The source of transistor 626 is coupled to the drainof transistor 628, which can be a NMOS transistor. The source oftransistor 628 can be coupled to the drain of transistor 630, which canbe a NMOS transistor. The source of transistor 630 is coupled to avoltage source, such as, for example, Vnwl (or, e.g., Vss or another lowvoltage source). In addition, transistor 632, which can be, for example,a NMOS transistor, is disposed in parallel with transistor 630. Thus,the source of transistor 632 can be connected to the same voltage sourceas that of transistor 630, such as, for example, Vnwl (or, e.g., Vss oranother low voltage source), and the drain of transistor 32 can beconnected to the source of transistor 628. The circuit 620 can alsoinclude a level shifter 640 that receives the PHF signal from circuit610. In some embodiments, the level shifter 640 shifts the high voltagelevel of the PHF signal. For example, if the PHF signal from circuit 610is at Vccp, which can be, for example, 3.2 volts, the level shifter 640outputs a gate drive signal 642 that is higher in value such as, forexample, Vccp2.

As seen in FIG. 6, the gates of transistors 622 and 630 receive thetiming control signal R2ACF. When the timing signal R2ACF is high,transistor 622 is OFF to isolate the PH signal line from the highvoltage source (e.g., Vccp2) and the transistor 630 is ON to pull downthe PH signal line to the value of the low voltage source Vnwl (or,e.g., Vss or another low voltage source) via the stabilization circuit625. As discussed above, the stabilization circuit 625 can include twocontinuously gated transistors 626 and 628 that are connected in series.The continuously gated transistors 626 and 628 are connected between thePH signal line and the drains of transistors 630 and 632. Becausetransistors 626 and 628 are always ON, the voltage PH signal line ispulled down to Vnwl (or, e.g., Vss or another low voltage source) whenthe transistor 630 or the transistor 632 is ON. The gate of transistor626 can be connected to a high voltage source that can provide a voltagein a range of 1.5 volts to 4.7 volts (e.g., Vccp2, Vccp, Vcc or anotherhigh voltage source) and the gate of transistor 628 is connected to ahigh voltage source that can provide a voltage in a range of 1.5 voltsto 4.7 volts (e.g., Vccp2, Vccp, Vcc or another high voltage source). Insome embodiments, the gate of transistor 626 is connected to a voltagesource that is at a higher voltage than the gate of transistor 628. Forexample, the gate of transistor 626 can be connected to Vccp2 and thegate of transistor 628 can be connected to Vccp or Vcc. In someembodiments, the gate of transistor 628 is connected to a voltage sourcethat is at a higher voltage (e.g., Vccp2) than the gate of transistor626 (e.g., Vccp, Vcc). In some embodiments, the gate of transistor 626is connected to a voltage source that is at a same voltage level as thatof the gate of transistor 628. The NMOS transistors 626 and 628 providemore reliability to FXD 600 circuit by providing a resistive path forthe leakage current going through transistor 630 and/or transistor 632to create a voltage drop in the leakage current path when one or bothtransistors 630 and 632 are OFF.

When the timing signal R2ACF is low, transistor 630 is OFF to isolatethe PH signal line from the low voltage source Vnwl (or, e.g., Vss oranother low voltage source), and the transistor 622 is ON to connect thehigh voltage source (e.g., Vccp2) to the transistor 624. The value ofthe PH signal line when the timing signal R2ACF is low is based on theoutput gate drive signal 642, which is received by the gates oftransistors 624 and 632. When the PHF signal is high (e.g., Vccp, Vcc,etc.), the transistor 624 is OFF and the transistor 632 is ON. Withtransistor 632 ON, the voltage of the PH signal line is pulled to thelow voltage source Vnwl (or, e.g., Vss or another low voltage source)because transistors 626 and 628 are ON. When the PHF signal is low(e.g., at Vnwl, at Vss or at another low voltage value), the transistor632 is OFF and the transistor 624 is ON. With R2ACF low and transistor622 ON, the PH signal line is pulled up to the high voltage source(e.g., Vccp2). The PH phase signal is output from the FXD 600 toactivate a local word line WL of the appropriate SWD or SWDs. Table 3provides a logic table for the FXD 600 (the “--” indicates that thevalue H or L of that input signal does not matter to output values.

TABLE 3 INPUT OUTPUT RF0 R1AC R2ACF PHF PH 1A L — — H L 1B — L — H L 2 HH L L H 3 H H H L L

In some embodiments, rows 1A and 1B in Table 3 can correspond to a timeperiod prior to T0 and after T4 in FIG. 5B. During these periods, thecorresponding SWD (e.g., SWD 510, 520, 530, or 540) is in a pre-chargeor standby state. Row 2 can correspond to a time period between T0 andT3. During this time period, the corresponding SWD (e.g., SWD 510, 520,530, or 540) is in an active/intermediate voltage state and, asdiscussed above, the local word line WL (e.g., WL0, WL1, WL2, or WL3)follows the voltage on the respective global word line GR (e.g., GR0,GR1, GR2, or GR3). Row 3 can correspond to a time when both the PHF andPH signals are low if a delay in setting PHF0 to the high state afterPH0 goes to the low state is desired for any reason.

FIG. 7 is a flow diagram illustrating example method 700 for managingthe operation of the SWDs. The method 700 can be performed by processinglogic that can include hardware (e.g., processing device, circuitry,dedicated logic, programmable logic, microcode, hardware of a device,integrated circuit, etc.), software (e.g., instructions run or executedon a processing device), or a combination thereof. In some embodiments,the method 700 is performed by the processor 116 and/or anotherprocessor or processors that are external and/or internal to memorydevice 100. Although shown in a particular sequence or order, unlessotherwise specified, the order of the processes can be modified. Thus,the illustrated embodiments should be understood only as examples, andthe illustrated processes can be performed in a different order, andsome processes can be performed in parallel. Additionally, one or moreprocesses can be omitted in various embodiments. Thus, not all processesare required in every embodiment. Other process flows are possible.

At block 710, the processing device (e.g., processor 116 and/or anotherprocessor) generates a first phase signal and a second phase signal in amemory device. In some embodiments, as discussed above, the first phasesignal can be the PH phase signal and the second phase signal can be thePHF phase signal which are generated by a FX phase driver circuit (e.g.,FXD 600). At block 720, the processing device (e.g., processor 116and/or another processor) drives a local word line of the memory deviceto follow a global word line signal by setting the first phase signal ata first value prior to the global word line signal entering an activestate. For example, the local word line can be local word line WL (e.g.,WL0 to WLn) that is generated by a SWD and the global word line can beglobal word line GR (e.g., GR0 to GRn) that is generated by a MWD. Atransistor in a SWD (e.g., transistor 512 in SWD 510) can be turned ONso that the local word line WL (e.g., WL0) follows the global word lineGR (e.g., GR0), as discussed above. As seen in FIG. 5B, the PH phasesignal (e.g., PH0) is set to a high state (e.g., Vccp2) prior to theglobal word line (e.g., GR0) going to an active state (e.g., Vccp).

At block 730, the processing device (e.g., processor 116 and/or anotherprocessor) isolates the local word line from the global word line signalby setting the first phase signal at a second value only after theglobal word line signal has entered a pre-charge state. For example, thelocal word line can be local word line WL (e.g., WL0 to WLn) that isgenerated by a SWD and the global word line can be global word line GR(e.g., GR0 to GRn) that is generated by a MWD. A transistor in a SWD(e.g., transistor 512 in SWD 510) can be turned OFF so that the localword line WL (e.g., WL0) is isolated from the global word line GR (e.g.,GR0), as discussed above. As seen in FIG. 5B, the PH phase signal (e.g.,PH0) is set to a low state (e.g., Vnwl) only after the global word line(e.g., GR0) goes to a pre-charge state (e.g., Vnwl).

Although the present invention has been described with reference to thedisclosed embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from theinvention. For example, although exemplary embodiments have beenexplained with respect to NMOS transistors being the only transistorsused in the SWD, it will be understood that, in other embodiments, PMOStransistors may be substituted for NMOS embodiments and vice-versa, inwhich case the memory cells arrays and SWDs may be fabricated in ann-type substrate rather than a p-type substrate. Such modifications arewell within the skill of those ordinarily skilled in the art.Accordingly, the invention is not limited except as by the appendedclaims.

The above detailed descriptions of embodiments of the technology are notintended to be exhaustive or to limit the technology to the precise formdisclosed above. Although specific embodiments of, and examples for, thetechnology are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the technologyas those of ordinary skill in the relevant art will recognize. Forexample, although steps are presented in a given order, alternativeembodiments may perform steps in a different order. The variousembodiments described herein may also be combined to provide furtherembodiments.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustration,but well-known structures and functions have not been shown or describedin detail to avoid unnecessarily obscuring the description of theembodiments of the technology. Where the context permits, singular orplural terms may also include the plural or singular term, respectively.Moreover, unless the word “or” is expressly limited to mean only asingle item exclusive from the other items in reference to a list of twoor more items, then the use of “or” in such a list is to be interpretedas including (a) any single item in the list, (b) all of the items inthe list, or (c) any combination of the items in the list. Additionally,the terms “comprising,” “including,” “having,” and “with” are usedthroughout to mean including at least the recited feature(s) such thatany greater number of the same feature and/or additional types of otherfeatures are not precluded.

The processing device (e.g., processor 116 and/or anotherprocessor/controller) represents one or more general-purpose processingdevices such as a microprocessor, a central processing unit, or thelike. More particularly, the processing device can be complexinstruction set computing (CISC) microprocessor, reduced instruction setcomputing (RISC) microprocessor, very long instruction word (VLIW)microprocessor, or processor implementing other instruction sets, orprocessors implementing a combination of instruction sets. Processingdevice (e.g., controller 190, controller 140 and/or another controller)can also be one or more special-purpose processing devices such as anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), a digital signal processor (DSP), network processor,or the like. The processing device (e.g., controller 190, controller 140and/or another controller) is configured to execute instructions forperforming the operations and steps discussed herein.

The machine-readable storage medium (also known as a computer-readablemedium) on which is stored one or more sets of instructions or softwareembodying any one or more of the methodologies or functions describedherein. The machine-readable storage medium can be, for example, memorydevice 100 or another memory device. The term “machine-readable storagemedium” should be taken to include a single medium or multiple mediathat store the one or more sets of instructions. The term“machine-readable storage medium” shall also be taken to include anymedium that is capable of storing or encoding a set of instructions forexecution by the machine and that cause the machine to perform any oneor more of the methodologies of the present disclosure. The term“machine-readable storage medium” shall accordingly be taken to include,but not be limited to, solid-state memories, optical media and magneticmedia.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. The presentdisclosure can refer to the action and processes of a computer system,or similar electronic computing device, that manipulates and transformsdata represented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage systems.

The present disclosure also relates to an apparatus for performing theoperations herein. This apparatus can be specially constructed for theintended purposes, or it can comprise a general purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program can be stored in a computerreadable storage medium, such as, but not limited to, any type of diskincluding floppy disks, optical disks, CD-ROMs, and magnetic-opticaldisks, read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, or any type of media suitable forstoring electronic instructions, each coupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems can be used with programs in accordance with the teachingsherein, or it can prove convenient to construct a more specializedapparatus to perform the method. The structure for a variety of thesesystems will appear as set forth in the description below. In addition,the present disclosure is not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages can be used to implement the teachings of thedisclosure as described herein.

The present disclosure can be provided as a computer program product, orsoftware, that can include a machine-readable medium having storedthereon instructions, which can be used to program a computer system (orother electronic devices) to perform a process according to the presentdisclosure. A machine-readable medium includes any mechanism for storinginformation in a form readable by a machine (e.g., a computer). In someembodiments, a machine-readable (e.g., computer-readable) mediumincludes a machine (e.g., a computer) readable storage medium such as aread only memory (“ROM”), random access memory (“RAM”), magnetic diskstorage media, optical storage media, flash memory devices, etc.

It will also be appreciated that various modifications may be madewithout deviating from the disclosure. For example, one of ordinaryskill in the art will understand that various components of thetechnology can be further divided into subcomponents, or that variouscomponents and functions of the technology may be combined andintegrated. In addition, certain aspects of the technology described inthe context of particular embodiments may also be combined or eliminatedin other embodiments. Furthermore, although advantages associated withcertain embodiments of the new technology have been described in thecontext of those embodiments, other embodiments may also exhibit suchadvantages and not all embodiments need necessarily exhibit suchadvantages to fall within the scope of the technology. Accordingly, thedisclosure and associated technology can encompass other embodiments notexpressly shown or described.

I/We claim:
 1. An apparatus, comprising: a word line circuit connectedto a word line of a memory device and configured to drive the word lineto one of an active state, an intermediate voltage state, or apre-charge state; and a processing device operatively coupled to theword line circuit and configured to drive the word line to theintermediate voltage state prior to entering the pre-charge state whentransitioning from the active state to the pre-charge state so as toprovide row hammer stress mitigation between adjacent local word linesin the memory device, wherein a voltage level of the intermediatevoltage state is below a voltage level of the active state and above avoltage level of the pre-charge state.
 2. The apparatus of claim 1,wherein the voltage level of the intermediate voltage state is in arange of 0.25 volts to 0.75 volts.
 3. The apparatus of claim 1, whereinthe voltage level of the intermediate voltage state is 0.5 volts.
 4. Theapparatus of claim 1, further comprising: a phase driver configured togenerate a first phase signal and a second phase signal, wherein theword line includes a local word line and the word line circuit includesa sub-word line driver that is connected to a global word line, andwherein the processing device is operatively coupled to the phase driverand configured to drive the local word line between a value of theglobal word line and a value of a low voltage source based on the firstand second phase signals.
 5. The apparatus of claim 4, wherein thesub-word line driver includes a PMOS transistor to pull-up the localword line to the value of the global word line and a NMOS transistor topull-down the local word line to the value of a low voltage source basedon the first and second phase signals.
 6. The apparatus of claim 4,wherein the sub-word line driver exclusively uses NMOS transistors. 7.The apparatus of claim 6, wherein the phase driver includes, a firstdriver circuit configured to set the first phase signal to a first highstate value that is higher than the active state voltage level of thelocal word line to drive the local word line to one of the active statevoltage level or the intermediate voltage state voltage level, and asecond driver circuit configured to set the second phase signal to asecond high state value to drive the local word line to the value of thelow voltage source.
 8. The apparatus of claim 7, wherein the firstdriver circuit includes a stabilization circuit configured to provide aresistive path for a leakage current in the first driver circuit whenthe first phase signal is at the first high state value.
 9. Theapparatus of claim 8, wherein the stabilization circuit includes a firstcontinuously gated transistor and a second continuously gatedtransistor, and wherein a gate voltage of the first continuously gatedtransistor is in a range of 3.8 volts to 4.7 volts, and a gate voltageof the second continuously gated transistor is in a range of 1.5 voltsto 3.2 volts.
 10. The apparatus of claim 4, wherein the sub-word linedriver includes a pull-up circuit configured to receive the first phasesignal and a global word line signal, the pull-up circuit furtherconfigured to drive the local word line to follow the global word linesignal when the first phase signal is at a first value and isolate thelocal word line from the global word line signal when the first phasesignal is at a second value, wherein the processing device isoperatively coupled to the phase driver circuit, the processing deviceconfigured to, set the first phase signal to the first value prior tothe global word line signal having the active state voltage level, andset the first phase signal to the second value only after the globalword line signal has the pre-charge state voltage level.
 11. Theapparatus of claim 10, wherein the sub-word line driver includes, apull-down circuit that is configured to receive the second phase signaland a low voltage signal, the pull-down circuit further configured todrive the local word line to follow the low voltage signal when thesecond phase signal is at a third value and isolate the local word linefrom the low voltage signal when the second phase signal is at a fourthvalue, and wherein the processing device sets the second phase signal tothe third value at a same time as the first phase signal is set to thefirst value and sets the second phase signal to the fourth value at asame time as or after the first phase signal is set to the second value.12. The apparatus of claim 1, further comprising: a RF driver circuitconfigured to provide a first row factor signal and a second row factorsignal, wherein the word line circuit includes a main word line driverthat includes, a pull-up circuit configured to receive the first rowfactor signal and configured to drive the global word line to the activestate voltage level when the first row factor signal is at a first valueand isolate the global word line from the active state voltage levelwhen the first row factor signal is at a second value, and anintermediate voltage circuit configured to receive the first and secondrow factor signals, the intermediate voltage circuit further configuredto drive the global word line to follow a value of the second row factorsignal when the first row factor signal is at the second value, whereinthe value of the second row factor signal is at the intermediate voltagestate voltage level.
 13. The apparatus of claim 12, wherein the RFdriver circuit receives a first timing signal and a second timingsignal, wherein the RF driver circuit is configured such that the secondrow factor signal has the intermediate voltage state voltage level whenthe first timing signal is at a first state and the second timingsignals is at a second state that is opposite the first state.
 14. Anapparatus, comprising: a plurality of word line circuits, each of theword line circuits configured to drive a respective word line to one ofan active state, an intermediate voltage state, or a pre-charge state; aprocessing device operatively coupled to each of the word line circuits,the processing device configured to drive the respective word line tothe intermediate voltage state prior to entering the pre-charge statewhen transitioning from the active state to the pre-charge state so asto provide row hammer stress mitigation between adjacent local wordlines in a memory device, wherein a voltage level of the intermediatevoltage state is below a voltage level of the active state and above avoltage level of the pre-charge state.
 15. The apparatus of claim 14,wherein the voltage level of the intermediate voltage state is in arange of 0.25 volts to 0.75 volts.
 16. The apparatus of claim 14,further comprising: a plurality of phase drivers, each phase driver ofthe plurality of phase drivers configured to generate a first phasesignal and a second phase signal, wherein each word line includes alocal word line and each of the plurality of word line circuits includesa sub-word line driver that is connected to a corresponding global wordline, and wherein the processing device is operatively coupled to eachphase driver of the plurality of phase drivers and configured to drivethe respective local word line between a value of the correspondingglobal word line and a value of a low voltage source based on thecorresponding first and second phase signals.
 17. The apparatus of claim16, wherein each phase driver of the plurality of phase drivers isconnected to a predetermined number of sub-word line drivers, where eachof the predetermined number of sub-word line drivers connects to adifferent global word line.
 18. The apparatus of claim 17, wherein thepredetermined number of sub-word line drivers is seven.
 19. Theapparatus of claim 16, wherein each of the plurality of phase diversincludes, a first driver circuit configured to set the first phasesignal to a first high state value that is higher than the active statevoltage level of the local word line to drive the local word line to oneof the active state voltage level or the intermediate voltage statevoltage level, and a second driver circuit configured to set the secondphase signal to a second high state value to drive the local word lineto the value of the low voltage source, and wherein the first drivercircuit includes a stabilization circuit configured to provide aresistive path for a leakage current in the first driver circuit whenthe first phase signal is at the first high state value.
 20. Theapparatus of claim 14, further comprising: a plurality of RF drivercircuits, each RF driver circuit configured to provide a first rowfactor signal and a second row factor signal, wherein each word linecircuit of the plurality of word line circuits includes a main word linedriver that includes, a pull-up circuit configured to receive the firstrow factor signal and configured to drive the respective global wordline to the active state voltage level when the first row factor signalis at a first value and isolate the global word line from the activestate voltage level when the first row factor signal is at a secondvalue, and an intermediate voltage circuit configured to receive thefirst and second row factor signals, the intermediate voltage circuitfurther configured to drive the respective global word line to follow avalue of the second row factor signal when the first row factor signalis at the second value, wherein the value of the second row factorsignal is at the intermediate voltage state voltage level.